The invention relates to a process for the production, with a continuous supply of the substrate (fed batch) of a sophoroside composition by fermentation. Sophorosides are e.g. used in cosmetology, in dandruff treatment for hair and as a bacteriostatic agent in deodorants, particularly in lactone form (EP-B-209783.
It is stated in U.S. Pat. Nos. 3,205,150 and 3,312,684 that a quantity of sophorosides was produced by a Fermentation process using a Torulopsis bombicola culture the strain presently classified as Candida bombicola.
Sophorosides are considered as being a mixture of the compounds represented by Formulas (1) and (2): ##STR1## in which R.sup.1 represents hydrogen or an acetyl group and R.sup.2 hydrogen or an alkyl group having 1 to 9 carbon atoms, when R.sup.3 is a saturated hydrocarbon radical with 7 to 16 carbon atoms, or R.sup.2 represents hydrogen or a methyl group, when R.sup.3 is an unsaturated hydrocarbon radical with 13 to 17 carbon atoms.
These compounds can be used as cleaning agents and emulsifiers and have excellent hygroscopic and hydrophilic properties due to the sophorose group and hydrophobic properties as a result of the Fatty acid.
However, sophorosides are a group of numerous homo logs and the formation ratio of these homologs varies as a function of their substrate, e.g. a hydrocarbon source, as well as the fermentation conditions (FR-A-2399438). Consequently, the properties and functions of these compounds vary with the ratios of the homologs, bearing in mind that use is generally made of a group of said homologs and it has hitherto been difficult to be able to produce a product having a given ratio using a fermentation process.
The prior art is illustrated by the document "Journal of the Americal Oil Chemists Society, vol.65, No. 9, September 1988, Champaign, Ill., USA, pages 1460-1466: H. J. ASMER et al-- "Microbial production, structure elucidation and bioconversion of sophorose lipids."
Sophorosides are generally prepared in the presence of a substrate, such as is e.g. described in U.S. Pat. No. 3,205,150. for example, said substrate can be in the form of hydrocarbons, saturated or unsaturated fatty acids, acid esters including glycerides, vegetable oils such as soybean oil, etc. Supply generally takes place discontinuously at time intervals of approximately 12 to 24 hours and with a quantity of approximately 2% by weight, based on the initial reaction volume, for each addition.
It is stated that the presence of a higher substrate quantity (3 to 4% approximately) leads to a reduction in the yield of sophorosides produced. Moreover, 24 to 48 hours following the final substrate addition, no supplementary conversion is observed.
This batch production process is also described in U.S. Pat. No. 4,297,340, where a substrate quantity (150 g) is added every 24 hours for 6 days, the total culture production time being 7 days.
These discontinuous supply processes make it possible to reach final crude sophoroside production levels not exceeding 23%, so that yields are limited. The reason for this limitation is the lipolytic capacity of the microorganism, which transforms the residual esters or oils of the fermentation medium into fatty acids. These fatty acids are not inhibitors to microorganism growth, but they are liable to significantly affect the sophoroside production speed, when already present in the medium.